1. Field of the Invention
The present invention relates generally to a transmitting/receiving apparatus and method using block coding in an OFDM (Orthogonal Frequency Division Multiplexing) mobile communication system, and in particular, to a transmitting/receiving apparatus and method for reducing through block coding a high PAPR (Peak-to-Average Power Ratio) resulting from multiple sub-carriers.
2. Description of the Related Art
In general, OFDM is a two-dimensional multiplexing scheme of TDM (Time Division Multiplexing) and FDM (Frequency Division Multiplexing) in combination. An OFDM symbol is transmitted over sub-carriers forming a sub-channel.
By allowing the spectrum of each sub-carrier to overlap with orthogonality, OFDM increases the overall spectral efficiency. Since IFFT (Inverse Fast Fourier Transform) and FFT (Fast Fourier Transform) provide OFDM modulation and demodulation, an efficient digital implementation of a modulator and a demodulator can be carried out. Furthermore, due to its robustness against frequency-selective fading and narrow-band interference, OFDM is effective for high-speed data transmission for the current European digital broadcasting and large-volume radio communication systems based on such standards such as IEEE 802.11a, IEEE 802.16 and IEEE 802.20.
Since an OFDM communication system transmits data over multiple sub-carriers, the amplitude of a final OFDM signal is the sum of the amplitudes of the sub-carriers. Hence, if each sub-carrier has the same phase, a very high PAPR results.
With a very high PAPR, an amplifier exceeds its linear operation range and a signal suffers from distortion after being processed by the amplifier in a typical OFDM communication system. Consequently, a transmitted OFDM signal does not have a constant amplitude variation due to the phase difference between sub-carriers. Moreover, backoff from an operating point from the maximum power available from the amplifier increases thereby decreasing amplifier efficiency and increasing power consumption. The high PAPR signal reduces the efficiency of a linear amplifier and forces the operating point of a non-linear amplifier into a non-linear region. As a result, the high PAPR introduces both in-band distortion and out-of-band spectrum regrowth.
Many techniques have been proposed for PAPR reduction. One of them is to use a pre-distorter having the non-linear and inverse function characteristics of a power amplifier to be linearized, for avoiding signal distortion. Also, a non-linear amplifier can be made to operate in a linear region through a backoff from its operating point. However, these methods have the shortcomings of circuit complexity in a high frequency band, low power efficiency, and cost increases.